Coiled body numbers in the Arabidopsis root epidermis are regulated by cell type, developmental stage and cell cycle parameters

We have used whole mount immunofluorescence labelling with the antibody 4G3 , raised against the human snRNP-specific protein U2B ", and whole mount in situ hybridization with an anti-sense probe to a conserved region of U2 sn RNA, in combination with confocal microscopy, to examine the organization o f spliceosomal components throughout the development of the Arabidopsis tha liana root epidermis, We show that the number of coiled bodies, nuclear org anelles in which splicing snRNPs and snRNAs concentrate, is developmentally regulated in the Arabidopsis root epidermis, Firstly, there is a progressi on from a small number of coiled bodies in the quiescent centre and initial cells, to a larger number in the cell division zone, returning to a lower number in the cell elongation and differentiation zone. Secondly, trichobla sts (root-hair forming epidermal cells) have on average 1.5 times more and often smaller coiled bodies than atrichoblasts (hairless epidermal cells). Moreover, we have shown that these differences in coiled body numbers are r elated to differences in cell cycle stage, cell type and developmental stag e, but are not due to differences in nucleolar or general metabolic activit y per se, We discuss possible explanations, including a model in which coil ed bodies coalesce during interphase, for the developmental dynamics of coi led bodies.